FOUS30 KWBC 160816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Wed Jul 16 2025

Day 1
Valid 12Z Wed Jul 16 2025 - 12Z Thu Jul 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MID-ATLANTIC STATES, THE CENTRAL PLAINS, AND THE UPPER MIDWEST...

...Central High Plains through the Great Lakes... 
Return flow around a broad mid-level ridge centered off the 
Atlantic coast will continue to result in a plume of exceptional 
moisture and instability rotating across much of the CONUS. Today, 
this plume of thermodynamics will stretch from Texas into the Upper
Midwest and then into New England, where PWs of 1.5 to 2.25 inches
overlapping pools of MUCAPE exceeding 2000 J/kg will reside. Into 
this plume, a dissipating stationary front will drop southeast, 
while a secondary front approaches from the NW in response to 
subtle height falls in response to broad but increasing troughing 
over the Northern Plains. This will result in squeezed mid-level 
flow from WSW to ENE from Texas into New England, through which 
multiple shortwaves will traverse along the boundary to 
additionally enhance ascent. Although much of the area will 
experienced scattered convection, there is likely to be an axis of 
enhanced organization from Kansas into Wisconsin.

In this region, multiple MCSs driven by connectively enhanced 
shortwaves will move across these areas with focused heavy rainfall, 
aided by waves of low pressure which may develop along the front. 
Although there continues to be some latitudinal and longitudinal 
spread with the placement of these MCSs which will be the primary 
driver of the flash flood risk, a slowly veering 30-40kt LLJ 
emerging from the Southern Plains will provide the focus for 
development through convergence and isentropic lift. The models 
suggest potentially two foci for heaviest rain, one in Kansas and a 
second axis from southern MN into WI, but anywhere across this 
region could experience short term training through Corfidi vectors 
that are aligned to the mean wind and the front (MN and WI) or anti-
parallel to the mean wind (KS). With rain rates likely reaching 1-
2"/hr, if not locally higher, this could result in instances of 
flash flooding and the inherited SLGT risk was modified for new 
guidance to cover the highest probabilities for 3" and locally 5" today.

...Ohio Valley into the Mid-Atlantic... 
Farther east into the thermodynamic plume mentioned above, a 
secondary maxima of heavy rainfall is likely from Ohio into 
Pennsylvania and surrounding areas. This is where a shortwave is 
progged to track overhead during peak heating and maximum 
instability. This will not only drive enhanced ascent, but also 
accelerate bulk shear to 30-35 kts which will force better storm 
organization. 850mb inflow across this area will also strengthen, 
potentially reaching 30-35 kts which will be 1.5 times the mean 
0-6km wind, a signal for strong convergence. Although storms that 
develop should remain progressive to the east, slower storm motions
during convective initiation are also possible. Regardless of the 
exact behavior, multiple rounds are likely in many areas, and each 
one will rainfall rates of around 2+"/hr (20-40% chance), leading 
to total rainfall of 2-4" with locally higher amounts possible 
(10-20% chance of 5" in both REFS and HREF, despite latitudinal 
placement differences.) This falling atop saturated soils from 
recent heavy rainfall will likely result in instances of flash 
flooding once again today.

...Gulf Coast... 
Invest 93L exiting the northern Florida peninsula this morning 
will drift westward into the northern Gulf on Wednesday. The 
accompanying mid-level inverted trough/tropical wave will be forced
due west as it remains south of an elongated ridge extending from 
the Atlantic Ocean. There continues to be quite a bit of spread of 
intensity of the accompanying surface reflection to this feature 
(and NHC continues a 40% chance of development) but the track 
guidance has converged moving just south of the coast through the 
next few days. Regardless of the exact track and development of 
this system, the accompanying tropical moisture plume (PWs 2.25 to 
2.5 inches, as much as +3 sigma according to the GEFS) will spread 
onshore to support showers and thunderstorms with heavy rainfall 
rates of 2-3"/hr. There continues to be uncertainty into how far 
north any of this moisture will spread due to subsidence/dry air 
beneath the ridge to the north, but guidance has begun to focus a 
relative maxima across southeast LA, and potentially as far east as
Mobile Bay, AL. In this corridor, both the HREF and REFS 
probabilities for 5"/24 hrs exceed 25%, and the inherited SLGT risk
has been cosmetically adjusted for this area, embedded within a 
larger surrounding MRGL risk.

...Desert Southwest... 
Active convection is likely again today across the Southwest as 
the mid-level ridge weakens and weak impulses, some of which are 
convectively enhanced by thunderstorms from Tuesday, move across 
the region. PWs are expected to continue to be above 1.25", highest
across southern AZ, but with a slow decrease in intensity and 
coverage of this PW plume. Additionally, probabilities for CAPE 
exceeding 500 J/kg are lower and confined east of the greatest 
moisture today, indicating that coverage and intensity of 
thunderstorms should be less than what occurred Tuesday. Despite 
that, convection should still be relatively widespread, but 
possibly displaced north of previous activity, although any weak 
remnant MCVs could enhance local ascent leading to local flash 
flood impacts, most likely should any thunderstorms with 0.5"/hr 
rain rates track across burn scars or sensitive terrain.

Weiss

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